1. Field of the Invention
The present invention relates to a method of forming a film pattern on a substrate, and a panel substrate used in display panel such as liquid crystal.
2. Description of the Prior Art
In panel substrates or the like having light-transparent electrodes to be used in printed circuit board, integrated circuit, liquid crystal display panel or the like, many methods are known and practically used for forming a conductive film in a desired pattern. The most widely known method is the process by photolithograph technology and chemical etching. According to this method, a conductive film is formed on a substrate on which a pattern is to be formed, and a photosensitive resin (photoresist) film is formed on this conductive film. This photoresist film is disposed with light through a photomask in a predetermined pattern. The photoresist in the disposed area is made insoluble in solvent, and the soluble part is removed by solvent. Afterwards, the film is etched by chemicals to obtain the predetermined pattern. This method is high in precision, and is capable of forming a pattern in a considerably large film thickness.
One of the other methods is the lift-off method by using a photoresist. In this method, same as in the foregoing method, the photoresist film is formed in a pattern, but what is different is that the photoresist film is formed in a predetermined pattern on the substrate in the first place. Later, a film of a desired material is disposed, and the insoluble photoresist pattern is dissolved and removed together with the film of desired material thereon by using other chemicals. To make lift-off easy, ultrasonic energy or other mechanical force may be used sometimes auxiliarily. This method is also employed widely.
In the method of forming a resist film pattern, the process of making use of printing is also known in the fabrication of printed circuit board. A method of directly cutting off the film on the substrate mechanically is also known. Or a method of destroying the film by laser and forming a pattern is known, too.
In such pattern forming methods, there are specific demerits. In the method using photoresist, the photoresist pattern forming step is complicated and troublesome. The step is very long including application of uniform photoresist film, prebaking, exposure, development, postbaking and others, the setting of conditions is difficult and unstable, and many expensive chemicals are needed. Besides, huge equipment and an enormous cost are required for treatment of the spent chemicals. In addition, many expensive facilities are used in each step. Moreover, in the etching step using chemicals, there are many problems in the control of process conditions, waste liquid treatment, facility cost and others. In the lift-off method, although the etching step is not needed, a heat treatment for enhancing the adhesion strength of the film to the substrate after forming the film cannot be sufficiently performed because of the heat resistance of the resin and fixing. The method of cutting off the film mechanically is handy, but the substrate itself will be injured, and the precision is poor, and it may be applied only in a limited range of products. The laser method has its own problems in low machining speed and poor linearity of the cut section.